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Role of allosteric switch residue histidine 195 in maintaining active-site asymmetry in presynaptic filaments of bacteriophage T4 UvsX recombinase.

Authors :
Farb JN
Morrical SW
Source :
Journal of molecular biology [J Mol Biol] 2009 Jan 16; Vol. 385 (2), pp. 393-404. Date of Electronic Publication: 2008 Nov 12.
Publication Year :
2009

Abstract

Recombinases of the highly conserved RecA/Rad51 family play central roles in homologous recombination and DNA double-stranded break repair. RecA/Rad51 enzymes form presynaptic filaments on single-stranded DNA (ssDNA) that are allosterically activated to catalyze ATPase and DNA strand-exchange reactions. Information is conveyed between DNA- and ATP-binding sites, in part, by a highly conserved glutamine residue (Gln194 in Escherichia coli RecA) that acts as an allosteric switch. The T4 UvsX protein is a divergent RecA ortholog and contains histidine (His195) in place of glutamine at the allosteric switch position. UvsX and RecA catalyze similar strand-exchange reactions, but differ in other properties. UvsX produces both ADP and AMP as products of its ssDNA-dependent ATPase activity--a property that is unique among characterized recombinases. Details of the kinetics of ssDNA-dependent ATP hydrolysis reactions indicate that UvsX-ssDNA presynaptic filaments are asymmetric and contain two classes of ATPase active sites: one that generates ADP, and another that generates AMP. Active-site asymmetry is reduced by mutations at the His195 position, since UvsX-H195Q and UvsX-H195A mutants both exhibit stronger ssDNA-dependent ATPase activity, with lower cooperativity and markedly higher ADP/AMP product ratios, than wild-type UvsX. Reduced active-site asymmetry correlates strongly with reduced ssDNA-binding affinity and DNA strand-exchange activity in both H195Q and H195A mutants. These and other results support a model in which allosteric switch residue His195 controls the formation of an asymmetric conformation of UvsX-ssDNA filaments that is active in DNA strand exchange. The implications of our findings for UvsX recombination functions, and for RecA functions in general, are discussed.

Details

Language :
English
ISSN :
1089-8638
Volume :
385
Issue :
2
Database :
MEDLINE
Journal :
Journal of molecular biology
Publication Type :
Academic Journal
Accession number :
19027026
Full Text :
https://doi.org/10.1016/j.jmb.2008.11.003